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1、外文翻譯INTRODUCTIONTOPRESTRESSCONCRETEBasicConceptsofPrestressingPrestressingconcreteisbasicallyconcreteinwhichinternalstressesofsuitablemagnitudeanddistributionareintroductionsothatthestressesresultingfromexternalloadsareconteractedtoadesireddegree.inreinforcedconcretemembers,thepr
2、estressiscommonlyintroducedbytensioningthesteelreinforcement.Theearliestexamplesofwoodenbarrelconstructionbyforce-fittingofmetaltyresonwoodenwheelsindicatethattheartofprestressinghasbeenpracticedfromancienttimes.thetensilestrengthofplainconcreteisonlyafractionofitscompressivestre
3、ngthandtheproblemofitbeingdeficientintensilestrengthappearstohavebeenthedrivingfactorinthedevelopmentofthecompositematerialknownas“reinforcedconcrete”.Thedevelopmentofearlycracksinreinforcedconcreteduetonon-compatibilityinthestrainsofsteelandconcretewasperhapsthestartingpointfort
4、hedevelopmentofanewmateriallike“presstressedconcrete“.theapplicationofpermanentcompressivestresstoamateriallikeconcrete,whichisstrongincompressionbutweakintension,increasestheapparenttensilestrengthofthatmaterial,becausethesubsequentapplicationoftensilestressmustfirstnullifytheco
5、mpressiveprestress.in1904Fresyssinetattemptedtosubstitutepermanentlyactingforcesinconcretetoresistthelasticforcesdevelopedunderloadsandthisideawaslaterdevelopedunderthenameof“prestressing”.thesignificantobservationwhichresultedfrompioneeringresearchworkonpretressedconcretewereNee
6、dforHighStrengthandConcrete1.Nessityofusinghighsteelandconcrete.2.Recognitionoflosserofprestressduetovariouscauses.heearlyattemptstousemindsteelinprestressedconcretewerenotsuccessfulsincetheworkingstressinmildsteelof120N/MM2moreorlesscompletelylostduetoelasticdeformation,creepand
7、shrinkageofconcrete.Thenomorelossofstressofstressinsteelisgenerallyabout100to240N/MM2anditisapparentthatifthislossofstressistobeasmallportionoftheintitlestress,thestressinstressinsteelintheintitlestagesmustbeveryhigh,about1200to2000N/MM2.therehighstressrangesarepossibleonlywithth
8、euseofhighstrengthsteel.Highstrengthconc
